Resettable snap action thermal limit switch



Feb. 5, 19 6 H. ULANET 2,394,121

RESETTABLE SNAP ACTION THERMAL LIMIT SWITCH Filed June 28, 1944 IN V EN TOR.

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lair/1g Patented m5. 5, 1946 RBSE'I'IABLE SNAP ACTION THERMAL LIMIT SWITCH Herman Ulanet, Newark, N. J.

Application June 28, 1944, Serial No. 542,498

6Claims.

This invention relates to improvements in electrical switches of the thermal limit type adapted to automatically open with a snap action when the temperature of a device or at a location served thereby exceeds a predetermined limit; and the invention has reference, more particularly, to a switch of such character which may be manually reset or closed.

This invention has for an object to provide a novel construction of manually resettable snap action thermal limit switch which is simple and compact in construction and economical to produce, and which is composed of a minimum number of easily assembled parts.

The invention has for a further object to provide a novel normally closed electrical switch adapted to be opened by a bi-metallic element which is responsive to temperature rise; the movable contact means of which comprises a fiat carrier spring which is fixed by its opposite ends to a support so as to be subjected to compression stress adapted to dispose the same in arcuate or bowed condition relative to the plane of its support, but nevertheless so as to be responsive to a proper directionally applied pressure, substantially perpendicular thereto, whereby it may be sprung or snapped across a center line from up-bowed to down-bowed position, or vice verse, to bring the movable contact means in closed or opened relation, as the case may be, to a relatively stationary contact means cooperative therewith; said bi-metalllc element being adapted, in operation, to deflect said carrier spring in direction to separate the movable and stationary contact means, and manually operable means being provided to deflect said carrier spring in direction to close together said movable and stationary contact means.

The invention has for another object to provide novel means for both mechanically supporting the movable and stationary contact means of the switch and for operatively relating and connecting the same in an electrical circuit to be controlled.

Another object of the invention is to provide means for sensitively adjusting to movable contact means relative to the thermostatic bi-metallic element, whereby to be actuated by the latter in response to the reaction thereof 'to a temperature of selected predetermined degree.

A further object of the invention is to provide a novel arrangement of and support for a manually operable switch reset means adapted for direct action upon the carrier spring of the movable contact means.

Other objects of this invention, not at this time more particularly enumerated, will be understood from the following detailed description of the same.

An illustrative embodiment of this invention is shown in the accompanying drawing, in which:

Fig. 1 is a top plan view of the switch according to this invention; Fig. 2 is a longitudinal sectional view thereof, taken on line 22 in Fig. 1; Fig. 3 is a horizontal sectional view thereof, taken on line 3-3 in Fig. 2; Fig. 4 is an end elevational view thereof, viewed from the left in Fig. l; and F18. 5 is a transverse sectional view thereof, taken on line 5-5 in Fig. 2.

Similar characters of reference are employed in the above described views, to indicate corresponding parts.

In the drawing, the reference character iii indicates a heated body, the temperature of which is desired to be electrically controlled through circuit including the thermal limit switch of this invention.

The switch structure comprises a bridge or bracket H, which is preferably provided at one end with a leg l2 having an angular foot-piece I; to engage the heated body l0, and so as to be suitably secured thereto, as e. g. by a fastening screw ll, whereby the bridge or bracket II, and its opposite end portion i5, is spaced outwardly from the adjacent surface of said heated body II.

The movable contact means of the switch comprises a metallic, and therefore electrically conductive, supporting frame plate l6 having a butt portion ll integral therewith; the latter being fixedly disposed to underlie the end portion ii of the bridge or bracket II, but being electrically insulated therefrom by an interposed block or sheet l8 of suitable insulation material. From its fixed butt portion I! said frame plate l8 extends forwardly in aligned but downwardly spaced relation to and beneath the main body of the bridge or bracket II.

Said frame plate I8 is, per se, of rigid or inflexible character, and, to assure such character, is preferably provided with means to stiiien the same against bending, such e. g. as stiffening flanges or ribs l9 disposed to project angularly from the plane thereof along its longitudinal margins. The transverse zone 20 intermediate the body of said frame plate It and its butt portion l1 provides a flexibly resilient section adapted to form a hinge-like connection about which the frame plate may be swng up or down, for purposes to be subsequently more particularly set forth. The tension of such hinge-like connection is such as to normally but yicldably upswing the frame plate relative to the horizontal plane of the fixed butt portion ll.

The body of said frame plate It is provided with an elongated opening 2! of suitable length and width extending longitudinally between inher and outer end portions thereof. Aligned with and extending longitudinally over said opening 25 is a fiat carrier spring 22 of a width somewhat less than the width of said opening 2!. The carrier spring 22 is fixedly anchored at its respective opposite end portions 23 to the body of said frame plate i6 by suitable fastening means, such e. g. as rivets 24. In such fixed relation, said carrier spring is subjected to a compression stress which is adapted to arcuately form or bow the body thereof relative to the flat plane of its fixed ends and that of the supporting frame plate [6 in one direction or the other. As thus bowed, the spring body is yieldably responsive to a proper directionally applied pressure perpendicular thereto, whereby it may be sprung or snapped across a center line or plane from up-bowed to down-bowed position, or vice versa. Said carrier spring 22 is provided, centrally of its arcuate or bowed portion with a contact element 25 projecting from its underside.

licieans is provided for connecting the frame plate ii and carrier spring 22 supported thereby to one side of an electrical circuit to be controlled he switch. Such means may comprise any table form and arrangement oi pole piece, illustratively shown comprises a terminal d sposed in electrical contact with the ortion ii of said frame plate N5, the same having an externally projecting ear 2! to which circuit wire 28 may be suitably mechanically nd electrically connected.

The stationary contactmeans of the switch comprises a metallic, and therefore electrically conductive, arm 29 having a butt portion 30 integral therewith; the latter being fixedly disposed to underlie the butt portion H and terminal plate 26 of the frame plate 46, but being electrically insulated therefrom by an interposed block or sheet 3! of suitable insulation material. From its fixed butt portion 30, said arm 29 extends forwardly in aligned but downwardly spaced relation to and beneath the frame plate i6 and carrier spring 22. Said arm 29 is provided, on its free end portion, which underlies the carrier spring 22 of the movable contact means, with a contact element 32 disposed to project from its upper side toward the contact element 25 of the movable contact means and in the path of movement of the latter.

Means is provided for connecting the stationary contact arm 29 to the Opposite side of an electrical circuit to be controlled by the switch; and such means may illustratively comprise a terminal plate 33 disposed in electrical contact with the butt portion of said arm 29 the same having an externally projecting ear 34 to which a circuit wire 35 may be suitably mechanically and electrically connected.

The thermostatic member of the switch comprises a bi-metallic plate 36 having a butt portion 31 which is fixedly disposed to underlie the butt portion 30 of the stationary contact arm 29, but which is electrically insulated therefrom by an interposed block or sheet 38 of suitable insulating material. From its fixed butt portion 31, said bi-metallic plate 36 extends forwardly in so on aligned but spaced relation to and beneath the movable and stationary contact means. The free end portion of said bi-metallic plate 36 extends beyond the free end portion of the stationary contact arm 29, so as to underlie a portion of the bowed carrier spring 22 of the movable contact means. Amxed to the free end portion of said bi-metallic plate 38 is an up-standing, electrically non-conductive push-finger 38, which is directed toward the carrier spring 22 of the movable oontact means. As related to and disposed beneath the movable and stationary contact means, said bi-metallic plate 36 is positioned at the under or inner side of the switch, and so as to lie closely adjacent to the surface of the heated body II), when the switch is mounted upon and aflixed to said body. Said bi-mctallic plate 36 is so characterized, that, when expanded by heat radiated from the body Ill, it is upwardly deflected, thus causing its free end portion to move toward the carrier spring 22 of the movable contact means.

To both secure the butt portions of the described elements of the switch and the interposed insulation together in assembled relation, as well as to. aflix the switch to the body l0, suitable fastening means is passed through the assembly. A preferable form of fastening means comprises one or more hollow rivets 40, the same being insulated from electrical contact with the movable and stationary contact means by surrounding sleeves of insulation material. Said hollow rivets 40 provide passages through which may be passed fastening screws 42 whereby to secure the butt or heel of the switch to the body [0 upon which it is desired to operatively mount the same.

The means for manually moving the carrier spring 22 of the movable contact means to switch closing position comprises a push button 43 of electrically non-conductive material, which is slidably mounted in a guide opening 44 with which the bridge or bracket II is provided; said push button being opposed to the intermediate portion of said carrier spring 22.

Means is provided for adjustably moving the frame plate i6 and its contact carrier spring 22 bodily toward and from the push finger 39 of the bi-metallic plate 36, whereby to selectively predetermine the temperature at which movement of the bi-metallic plate, when expanded and flexed by heat radiated from the body l0, will be sufiicient to carry the push finger 39 into switch opening engagement with the contact carrier spring 22. In an illustrative form of such means as shown, the same comprises an adjusting screw 45 threaded through the bridge or bracket H in opposition to the free end portion of the frame plate ii of the movable contact means; said screw 45 having an electrically nonconductive end portion 46 to bear upon said frame plate I8. By turning inwardly said adjusting screw 45, the frame plate I6 is swung downwardly about the flexible connection 20 by which it is joined to its butt portion l1, thereby moving the contact carrier spring closer to the push finger 39 of the bi-metallic plate, so that the latter becomes operative at a relatively low degree of temperature. By turning the adjusting screw 45 outwardly, the frame plate I6 and contact carrier spring is permitted to move farther away from the push finger 39 of the bi-metallic plate, so that the latter becomes operative at a relatively higher degree of temperature. Said adjusting screw 45 may be locked in adjusted position by the associated jam or lock nut 41.

In operation the switch is closed by pressing the push button 48, whereby spring the movable contact carrier spring 22 from an upwardly bowed condition to a downwardly bowed condition, as shown by dotted line representation in Figs. 2 and 5, whereby the contact element 25 is brought into circuit closing engagement with the contact element 32 of the stationary switch arm 29. The circuit controlled by the switch is used to energize suitable electrical heating means (not shown) for heating the body it. As the tempera-' ture of the heated body l rises, heat either radiating or conducted therefrom, or both, is transferred to the bi-metallic plate 38. Under the influence of the applied heat, said bi-metallic plate 36 is deflected or warped, whereby to cause its free end portion to rise toward the downwardly bowed movable contact carrier spring 22, until, on attaining a desired degree to which the switch is adjusted to respond, the push finger 39 engages and pushes upwardly upon the carrier spring 22, whereby to move the same past its center line or plane so that it springs, with a rapid snap action, back to upwardly bowed condition, and thus quickly separates the engaged contact elements '25 and 32 to thereby open the switch for interruption of the circuit controlled thereby.

After the switch is thus thermostatically opened, it can be reset to closed condition again, after a temperature drop in the body III, by again manipulating the push button 43 in the manner and with the switch closing action already above described.

Preferably the stationary contact arm 29, being fixed at one end only, provides a freely extending body portion, by which the contact element 32 is carried, which is suillclently resilient to yieldably react against the contact element 25, when the latter is lowered by down bowing of the carrier spring 22, with sufficient pressure to assure good electrical contact, but insufllcient to spring a the carrier spring upwardly across the center line or plate thereof.

If desired an electrical resistance may be applied to and around the bi-metallic element for electrically heating the same, whereby the switch may be operated as an overload circuit breaker, relay or thermal timer.

I am aware that some changes could be made in the above described thermal limit switch without departing from the scope of this invention as deflned in the herefollowing claims. It is therefore intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A resettable snap action thermal limit switch comprising supporting bracket means, a movable contact means, a stationary contact means, and a temperature sensitive element, said movable contact means comprising a frame plate having an elongated opening, a flat contact spring extending over said frame plate opening and fixed by its opposite ends to said frame plate so as to be subject to compression stress adapted to bow its body in one direction or the other relative to a normal center plane, a push button movably supported by said bracket means, said push button being manipulatable to bow said contact spring toward and in circuit closing engagement with said stationary contact means, and said temperature sensitive element having a push finger directed toward said contact spring and adapted upon deflection of said element by heat toengageandbowsaidcontactspringinthe opposite direction whereby to break circuit closing engagement thereof with said stationary conbi-metallic element in parallel plane spaced relation and respectively fixed by single ends thereof relative to said supporting bracket means and in electrically insulated relation thereto and to each other, said movable contact means comprising a relatively stationary rigid frame plate having a longitudinal opening therein, a flat contact spring extending endwise along said opening and fixed by its opposite ends to said frame plate so as to be subject to compression stress adapted to bow its intermediate portion in a single bend through the frame plate opening in one direction or the other relative to a normal center plane, a push button movably supported by said bracket means in opposition to one face of said intermediate portion of the contact spring, said push button being manipulatable to bow said contact spring toward and in circuit closing contact with said stationary contact means, and said bi-metallic element having a push-finger directed toward the opposite face of said intermediate portion of the contact spring and adapted upon deflection of said element by heat to engage and bow said contact spring in the opposite direction whereby to break contact thereof with said stationary contact means.

3. A resettable snap action thermal limit switch comprising supporting bracket means, a movable contact means, a stationary contact means and a temperature responsive bi-metallic element in parallel plane spaced relation and respectively fixed by single ends thereof relative to said supporting bracket means and in electrically insulated relation thereto and to each other, said movable contact means comprising a frame plate having a longitudinal opening therein, a flat contact spring extending endwise along said opening and fixed by its opposite ends to said frame plate so as to be subject to compression stress adapted to bow its intermediate portion in one direction or the other relative to a normal center plane, a push button movably supported by said bracket means, said push button being manipulatable to bow said contact spring toward and in circuit closing contact with said stationary contact means, and said bi-metallic element having a push-finger directed toward said contact spring and adapted upon deflection of said element by heat to engage and bow said contact spring in the opposite direction whereby to break contact thereof with said stationary contact means, and

means to adlustably space said frame plate and contact spring relative to said push-finger of said bi-metallic element for the purposes described.

4. A resettable snap action thermal limit'switch comprising supporting bracket means, a movable contact means, a stationary contact means and a temperature responsive bi-metallic element in parallel plane spaced relation and respectively fixed by single ends thereof relative to said supporting bracket means and in electrically insulated relation thereto and to each other, said movable contact means comprising a frame-plate having a rigid free body portion resiliently joined to its fixed end portion so as to be capable of bodily movement about the juncture thereof with said fixed end portion, said body portion having a longitudinal opening therein, a flat contact spring extending endwise along said opening and fixed by its opposite ends to said body portion so as to be subject to compression stress adapted to bow its intermediate portion in one direction or the other relative to a normal center plane, a push button movably supported by said bracket means, said push button being manipulatable to bow said contact spring toward and in circuit closing contact with said stationary contact means, said bi-metallic element having a pushfinger directed toward said contact spring and adapted upon deflection of said element by heat to engage and bow said contact spring in the opposite direction whereby to break contact thereof with said stationary contact means, and means to bodily adjust said frame plate body portion and said contact spring toward and from the normal position of the push-finger of said bi-metallic element.

5. A resettable snap action thermal limit switch comprising supporting bracket means, a movable contact means, a stationary contact means and a temperature responsive bi-metallic element in parallel plane spaced relation and respectively fixed by single ends thereof relative to said supporting bracket means and in electrically insulated relation thereto and to each other, said movable contact means comprising a frame plate having a rigid free body portion resiliently joined to its fixed end portion so as to be capable of bodily movement about the juncture thereof with said fixed end portion, said body portion having a longitudinal opening therein, a flat contact spring extending endwise along said opening and fixed by its opposite ends to said body portion so as to be subject to compression stress adapted to bow its intermediate portion in one direction or the other relative to a normal center plane. a push button movably supported by said bracket means, said push button being manipulatable to bow said contact spring toward and in circuit closing contact with said stationary contact means, said bimetallic element having a push-finger directed toward said contact spring and adapted upon deflection of said element by heat to engage and bow said contact spring in the opposite direction whereby to break contact thereof with said stationary contact means, and means to bodily adjust said frame plate body portion and said contact spring toward and from the normal position of the push finger of said bi-metallic element, said latter means comprising an adjusting screw threaded through said supporting bracket means to thrustingly engage the free end of said frame plate body portion.

6. A resettable snap action thermal limit switch comprising supporting means, a relatively stationary rigid frame plate having an elongated opening, a flat contact spring extending over said frame plate opening, said contact spring being fixed by its opposite ends to said frame plate so as to be subject to compression stress adapted to how the intermediate portion thereof extending between its fixed ends through the frame plate opening in one direction or the other relative to the plane of said frame plate, a stationary contact means to which one face of the bowable intermediate portion of said contact spring is opposed, a push button movably supported by said supporting means in opposition to the other face of the bowable intermediate portion of said contact spring, and a temperature sensitive element having a push finger directed toward that face of the bowable intermediate portion of said contact spring which opposes the stationary contact means.

HERMAN ULANET. 

